Studies are continuing on the mechanism by which donor bone marrow infused into ALS-treated mice produces specific increased survival of skin allografts. The effect of ALS and bone marrow on enhanced survival of skin is being studied in mice previously sensitized to either all donor antigens, the minor histocompatibility antigens of the donor but not the major antigens or third party (non-specific) antigens. The effect of marrow that has been frozen or stored for varying periods of time will also be studied in this system. Preliminary studies have shown that the survival of pancreatic islet cell allografts can also be enhanced in diabetic mice treated with ALS and given bone marrow. These studies are being extended to determine the most effective time for the graft to be transplanted in relation to ALS and marrow treatment.